A Safety Management System (SMS) is not a document. It is an approach to managing safety risk and assuring the effectiveness of safety risk mitigations. The Agency Safety Plan (ASP) is the transit agency’s document that formally defines its SMS processes and procedures. However, a transit agency may choose to develop and use additional SMS-related tools and documents, such as an SMS gap analysis checklist, SMS development plan, or SMS implementation plan, to help it assess its current safety management processes and plan for the development and implementation of SMS processes.

I had the same confusion as you about these three terms. I called the PTASP Technical Assistance Center to ask for clarification, and the person who helped me summarized it like this:

The PTASP is the rule/regulation (49 C.F.R. Part 673) that tell us to develop an ASP
The ASP is the actual document that our transit agency must develop
The SMS is not a document in and of itself, but an overarching system

The person then added that the ASP documents SMS processes and components, but the SMS itself is not a document. They said there's no such thing as an SMS document.

Hope that helps!

FTA uses the term Public Transportation Agency Safety Plan (PTASP) to refer to the PTASP regulation (49 C.F.R. Part 673) and its associated requirements.

FTA uses the term Agency Safety Plan (ASP) to distinguish the plan that transit agencies are required to develop from the PTASP regulation.

The PTASP regulation requires the adoption of Safety Management Systems (SMS) principles and methods. SMS is a formal, top-down, organization-wide approach to managing safety risk and assuring the effectiveness of a transit agency’s safety risk mitigation. Your ASP will document your agency’s SMS.